Tiantai Mountain (Chinese: 天台山; pinyin: Tiāntái Shān; Wade–Giles: T'ien T'ai shan) is in Tiantai County in Zhejiang Province, China, near the city of Taizhou. The mountain was made a national park on 1 August 1988. The Guoqing Temple on the mountain is the headquarters of the Tiantai sect of Buddhism and also a tourist destination. Tiantai Buddhism, named after the mountain, focuses on the Lotus Sūtra. The most prominent teacher of that school, Zhiyi, was based at the Guoqing Temple. Over many years it has been an important destination for pilgrims, especially from Japan. The mountain was visited by Saichō in 805 who went on to found the related school of Japanese Buddhism, Tendai.
According to one legend, Tiantai Mountain used to be carried by the giant turtle Ao, swimming in the ocean. When the goddess Nuwa had to cut off the turtle's legs in order to use them to support the falling sky, she moved the mountain to the dry land so that it would not sink in the ocean.
Mount Tai's highest peak, Huading Peak, reaches a height of 1,138 metres (3,734 ft).
One of nine remaining wild populations of Seven-Son Flower Heptacodium miconioides is located on Mount Tianta.